1. Field of the Invention
The present invention relates to a piezoelectric device of thin film type which can convert electric energy to mechanical energy, and vice versa. More specifically, the present invention relates to a piezoelectric device of thin film type which can be used for an actuator, a pressure sensor, a temperature sensor, an ink jet recording head, and the like.
2. Related Art
In general, the composition of a piezoelectric thin film is of a two-component system in which lead zirconate titanate (PZT) is a main component, or of a three-component system in which a third component is added to PZT.
However, we have never known such a precedent that attention was paid on the size of crystal grains contained in a thin film piezoelectric device and that the size of the crystal grains was controlled to the range as defined in the present invention.
For example, ferroelectrics in which PZT of a two-component system is used are disclosed in Applied Physics Letters, 1991, Vol. 58, No. 11, 1161-1163. Although this report discloses the properties of the ferroelectrics in detail, the evaluation of the properties of the ferroelectrics as piezoelectric devices are not conducted.
Further, Japanese Laid-Open Patent Publication No. 40035/1994 discloses a piezoelectric substance. However, it fails to describe the size-of crystal grains contained in a film of the piezoelectric substance.
Furthermore, Journal of The American Ceramic Society, 1973, Vol. 56, No. 2, 91-96 also discloses a film of a piezoelectric substance. It is described that the size of crystal grains contained in this film, observable by a scanning electron microscope is approximately 1.7 to 7 micrometers.